The subject matter disclosed herein relates to turbine buckets and, more specifically, to turbine buckets with high hot hardness shroud-cutting deposits.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. Energy is extracted from the gases in a high pressure turbine (HPT), which powers the compressor, and in a low pressure turbine (LPT), which powers an external shaft for marine and industrial applications, or powers a fan in a turbofan aircraft engine application.
One factor relevant to the efficiency of the gas turbine engine is the sealing arrangements between rotating and stationary components. For example, seals may be provided between the various stages of rotating components, such as turbine buckets, and corresponding stationary structures, such as housings or shrouds within which the rotating components turn. The efficiency and performance of gas and steam turbines may be affected by clearances between bucket squealer tip (e.g., blade tips or tip caps) and the stationary shrouds. Generally, the closer the stationary component surrounds the tips of the rotating component(s), the greater is the efficiency of the turbomachinery.
However, the clearance dimensions between the turbine bucket squealer tip and the shroud may vary during various operating modes of the turbine engine. One reason for this is the dissimilar thermal growth within the engine between the bucket squealer tips of the turbine bucket and the shroud surrounding them. In such a case, the high temperature of the working fluid may cause a thermal discrepancy between the shroud and the rotor blades, wherein the shroud is at a lower temperature than the turbine buckets. The time interval until the thermal equivalence between the shroud and the turbine buckets is restored may be referred to as the transient period. Furthermore, the clearance between the shroud and the turbine buckets can decrease during this transient period as the components reach their steady state conditions and dimensions and cause the interfacing surfaces to rub.
Seals on the stationary shroud surface can include a material designed to be wearable or abradable with respect to the turbine buckets rubbing against them. In such a system, during the transient period, the bucket squealer tip contacts or rubs against the shroud, causing the shroud material to abrade or flake off. This may reduce wear to the rotating elements and provide reduced clearances (thereby increasing sealing) compared to a non-abradable system. However, these sealing systems may still subject turbine buckets to various rubbing forces that may affect the original material on its bucket squealer tip.
Accordingly, alternative turbine buckets would be welcome in the art.